1. Field of the Invention
The present invention relates to a method of absorbing noise in a vehicle interior, and in particular to providing a seat cover with perforations optimized to facilitate noise absorption over a given range of frequencies.
2. Background Art
Noise in the interior of a vehicle is undesirable, and its reduction or elimination has long been a goal of vehicle interior designers. A variety of methods exist to try to achieve this goal. Since it is well known that porous materials are generally good absorbers of sound, vehicle interior components are often covered with porous materials to help quiet the vehicle""s interior. Carpeting is used on the floor and headliners are installed on the roof. Typically, thick porous materials faced with an open weave absorb sound better than thinner materials with impermeable faces. Often however, it is impractical to use thick materials in the interior of a vehicle, since interior space is limited. Moreover, a material with an open weave may lack other important functional characteristics such as high wear resistance. Hence, using thick, loosely woven carpets and headliners with open faces is not an adequate solution to the problem of vehicle interior noise.
One attempt to reduce engine noise before it reaches the vehicle interior is described in U.S. Pat. No. 5,744,763 issued to Iwasa et al. on Apr. 28, 1998. Iwasa et al. describes a sound absorbing material comprising a pulverized rubber layer and a covering layer. The sound absorbing material of Iwasa et al. is used on the inside of a vehicle hood panel, where noise waves from the engine pass through the covering material and are partially absorbed by the pulverized rubber. The material described in Iwasa et al. is designed for use in the engine compartment, and is specifically targeted to engine noise. Thus other noises external to the vehicle, such as road noise, are not reduced. Moreover, the pulverized rubber material necessarily adds bulk to the sound absorbing material, making it impractical for use in the interior of a vehicle.
Because the problem of noise in the interior of a vehicle cannot be eliminated by merely providing a sound absorbing material in the engine compartment, nor by altering the materials from which the carpet and headliner are made, other interior components have been analyzed for possible noise reduction improvements. For example, it is not uncommon for interior trim components to be made from, or at least covered with, a material that absorbs acoustic energy. Trim components on doors and package trays are two examples of interior components on which designers have focused their attention to try to reduce the noise problem. These efforts have met with limited success, and the problem of interior noise remains.
Another area of focus in the search to eliminate vehicle interior noise is the occupant seats, and in particular, the materials used to cover the seats. For purposes of absorbing noise, a thick, loosely woven cloth material is highly effective. Unfortunately, both aesthetics and functionality discourage the use of such a material. Moreover, even if a suitable cloth material is found, many designers prefer to use leather, particularly in higher-end vehicles.
Accordingly, it is desirable to provide a method of tuning the acoustical absorption in a vehicle interior that overcomes the shortcomings of the prior art, by taking advantage of the large surface area of the vehicle seats to reduce the noise from various sources while not using bulky and potentially expensive materials on the interior of the vehicle.
The design challenge overcome by the present invention is this: how to take advantage of the large surface area of the seatsxe2x80x94an excellent target for improving overall interior acoustic energy absorptionxe2x80x94while still maintaining the comfort and aesthetic benefits of leather or other non-cloth seat covers. Accordingly, it is desirable to provide a method of utilizing leather or other non-cloth seat covers to facilitate the absorption of noise in the interior of a vehicle, thereby taking advantage of the large surface area presented by the seats, while not sacrificing the comfort or aesthetic quality of the cover material.
The present invention provides a method of absorbing noise in the interior of a vehicle by creating a non-cloth covering for the seats which is capable of facilitating sound absorption. First, a specific noise frequency range is targeted. This frequency range is based on a number of factors including elimination of engine noise and maintaining an environment conducive to intelligible speech. Engines can generate low frequency noise of a few hundred Hertz, as well as higher frequency noise in the range of a few thousand Hertz. In addition, noises from the wind and other sources external to the vehicle contribute to these higher frequency noises. This is particularly annoying to passengers since many of these higher frequency noises make it difficult to understand spoken words. The frequency range targeted by the present invention is broad enough to encompass most of these noises; however, some of the lowest frequency performance may be sacrificed (if desired) to increase the range of frequencies absorbed.
Once the targeted frequency range is determined, perforations are formed in the seat cover material. The use of perforations in seat covers is common for purposes of increasing breathability. However, it was discovered that these same perforations have a positive impact on noise absorption in the interior of the vehicle. In the present invention, the seat cover perforations are specifically made at an optimal size and with an optimal arrangement for the targeted frequency range. The optimizing is based on a predetermined relationship between percent open area and absorption frequency. The percent open area is affected by two parameters: perforation size and perforation density. In general, increasing the percent open area increases the range of frequencies over which good sound absorption occurs; however, varying the size of the perforations for any given percent open area, also affects this range. Optimizing the noise absorption requires knowledge and application of each of these relationships.
Once the frequency range is chosen and the optimum size and arrangement are determined, the seat cover material is processed in a perforation machine. The machine, which essentially consists of large spike-laden rollers, receives the various pieces of material which comprise the seat cover. After processing in the perforation machine, the pieces are sewn together to form the finished seat cover which is then placed over a seat. The holes in the seat cover allow noise to pass into the interior structure of the seat where the acoustic energy is dissipated in the form of heat. Hence, the process requires very little added labor cost, and because there are no bulky sound absorbing materials added to the interior of the vehicle, there is no added material cost and no added weight. The benefit to cost ratio is accordingly high.
The process can be used to optimize only the seat cover, or it can be part of an overall acoustic energy management system within the vehicle interior. When used in the latter application, the noise reduction resulting from the optimized seat cover is analyzed first. Then other interior components are similarly analyzed. With this information, the designer determines an overall desired acoustic energy absorption level. Because the optimized seat cover provides an inexpensive method of absorbing acoustic energy, other interior components can be redesigned to eliminate costly sound absorbing materials. This results in a no net loss or even a net gain in sound absorption within the vehicle interior, while significantly reducing overall costs.
Accordingly, one aspect of the invention provides a process for reducing noise in the interior of a vehicle, while not significantly increasing costs or the weight of the vehicle.
Another aspect of the invention provides a process for optimizing the acoustic energy absorption within a vehicle interior, by inexpensively increasing the sound absorbing capability of the seats and simultaneously reducing the sound absorbing capability of other interior components by eliminating costly sound absorbing material from the other components.
A further aspect of the present invention provides a process for tuning acoustical energy absorption of a vehicle interior by determining a target noise frequency range to be absorbed, providing a cover material to cover the vehicle seats, selecting an optimal arrangement and size of perforations in the cover and forming them therein, and then covering the vehicle seats with this cover after the perforations are formed. This optimization process provides the additional advantage of employing perforations which are not visible to the naked eye, thereby ensuring that the aesthetics of the vehicle interior are not adversely affected. This innovation is contrary to the teaching of conventional seat engineering that holds that sound absorbing perforations cannot be used in seat covers because they detract from the aesthetics of the vehicle interior.
The above aspects and other aspects, objects, features and advantages of the invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.